is only a rough
distinction, which breaks down at many points.

Where shall we class sensation? Is it "mental" or "bodily"? Both
sciences study it. Physiology is perhaps more apt to go into the
detailed study of the action of the sense organs, and psychology to
concern itself with the classification of sensations and the use made
of them for recognizing objects or for esthetic purposes. But the line
between the two sciences is far from sharp at this point.

Speech, also, lies in both provinces. Physiology has studied the
action of the vocal organs and the location of the brain centers
concerned in speech, while psychology has studied the child's process
of learning to speak and the relation of speech to thought, and is
more apt to be interested in stuttering, slips of the tongue, and
other speech disturbances which are said to be "mental rather than
physical".

It would be hard to mention any activity that is mental without being
physical at the same time. Even thinking, which seems as purely mental
as any, requires brain action; and the brain is just as truly a bodily
organ as the heart or stomach. Its activity is bodily activity and
lies properly within the field of physiology.

{7}

But it would be equally difficult to mention any function that is
exclusively bodily, and not mental at the same time, in some degree.
Take digestion for example: the pleasant anticipation of food will
start the digestive juices flowing, before any food is physically in
the stomach; while in anger or fear digestion comes to a sudden halt.
Therefore we find physiologists interested in these emotions, and
psychologists interested in digestion.

We do not find any clean separation between our science and
physiology; but we find, on the whole, that psychology examines what
are called "mental" activities, and that it studies them as the
performances of the whole individual rather than as executed by the
several organs.

The Science of Consciousness

Typically, the activities that psychology studies are conscious
performances, while many of those falling to physiology are
unconscious. Thus digestion is mostly unconscious, the heart beat is
unconscious except when disturbed, the action of the liver is entirely
unconscious. Why not say, then, that psychology is the study of
conscious activities?

There might be some objection to this definition from the side of
physiology, which studies certain conscious activities itself--speech,